The invention relates to pipe couplings in general, and more particularly to improvements in pipe couplings of the type wherein a sealing ring between the outwardly extending flanges at the confronting ends of the pipes to be sealingly coupled to each other can be deformed by an annular clamping device which can be positioned to surround the flanges and to have its diameter reduced to thereby bias the flanges against the respective sides of the sealing ring.
U.S. Pat. No. 3,498,649 to Pfeuffer discloses a pipe clamping and centering device wherein the pipes which are to be sealingly coupled to each other end-to-end are provided with conical flanges. The clamping device comprises two conical sidewalls each of which is outwardly adjacent one of the conical flanges, and the flanges are separated from each other by an annular sealing ring having a trapezoidal or circular cross-sectional outline. The conicity of the radially outer portions of sidewalls of the clamping device is the same as that of the respective flanges, and the radially inner portions of the sidewalls are short cylinders which spacedly surround the external surfaces of the respective pipes. As a rule, pipes having conical flanges are made of relatively thin and hence readily deformable material (normally metallic sheet material). Therefore, once the pressure in the pipeline has risen to a relatively low level, the pipes tend to move axially and away from each other with resulting deformation of their flanges to thus establish clearances between the inner sides of the deformed flanges and the adjacent sides of the sealing ring. At the same time, the radially outermost portion of the ring is subjected to pronounced (often excessive) compressive stresses. Such situation is particularly likely to develop if the diameter of the clamping device is not or cannot be reduced to an extent which is necessary to ensure that the cylincrical radially inner portions of its sidewalls actually contact the external surfaces of the respective pipes. This establishes larger lever arms for the axial component of the force which is generated by the confined fluid medium and tends to move the pipes axially and away from each other, and the confined fluid tends to deform the flanges in a sense to separate their internal surfaces from the adjacent sides of the sealing ring. The clearances between the deformed flanges and the sealing ring result in leakage of the confined fluid medium.
A modified pipe coupling for two pipes one of which has a substantially conical flange and the other of which has a substantially radial flange is disclosed in U.S. Pat. No. 3,346,275 to Des Jardins. The cross-sectional outline of the clamping device is analogous to that of the clamping device in the pipe coupling of Pfeuffer, i.e., the clamping device has two sidewalls with conical radially outer portions and cylindrical radially inner portions which are remote from the external surfaces of the pipes. In addition, the pipe joint of Des Jardins must employ a specially designed insert which is to be placed next to the radially extending flange in order to be engaged by the conical radially outer portion of the respective sidewall of the clamping device.
The danger of undesirable deformation of flanges is even more pronounced if the flanges extend radially of the respective pipes, especially if the sidewalls of the clamping device are hollow conical frusta all the way from the radially inner to the radially outer ends. In such pipe couplings, the sidewalls of the clamping device engage only the external surfaces of the radially outer portions of the radially extending flanges to thus permit substantial deformation of the flanges all the way between their radially innermost and outermost ends. This entails the development of pronounced clearances between the inner sides of the deformed flanges and the adjacent sides of the sealing ring so that the confined fluid medium is even more likely to escape at the coupling.
German Utility Model No. 1 738 844 of Abel & Ebel KG discloses a sealing washer which is provided with a circumferentially extending harder portion. The washer is to be used in large-diameter pipes as a substitute for washers wherein a metallic ring is embedded in elastomeric material.
East German Pat. No. 105 496 of Karras et al. discloses a sealing ring which is to be used between a pipe and the flange of a boiler and has a radially inner portion in the form of an axially extending sealing lip.
Various conventional pipe couplings are shown in a publication which is distributed by the assignee of the present application and is entitled "Vorblatt zur Baureihe 4". Some of the pipe couplings which are shown in this publication are similar to those disclosed by Pfeuffer and Des Jardins.